Mainsail (noun)

1. The primary sail on a sailing vessel, typically located on the main mast.
2. A large sail that is the main source of propulsion for a sailing vessel.

Origin:

Derived from the old english word 'mǣnan' meaning 'to remain' and 'sāl' meaning 'sail'.

Examples:

1. The mainsail was hoisted to catch the wind and propel the ship forward.
2. The skipper trimmed the mainsail to optimize its shape and angle to the wind.
3. The mainsail was one of the largest and most important sails on the ship.
4. The crew had to reef the mainsail in order to reduce its surface area in strong winds.
5. The mainsail was the key to the ship's speed and performance on the open sea.